1. Field of the Invention
The present invention relates to image processing, and, in particular, to encoding video signals using run-length encoding.
2. Description of the Related Art
Many image compression algorithms are based upon the quantization of block transform coefficients. In such algorithms, an (N.times.N) block of image signals is transformed by a block transform, such as a slant, Haar, or discrete cosine transform (DCT). The resulting transform coefficients are quantized based typically on the visual importance of the various coefficients in the transformed block. Because of the energy compaction of the block transform followed by the quantization step, many zeros are generally found in the block of quantized transform coefficients. After the quantization of the coefficients, the block is scanned in order to create a sequential array of quantized coefficients.
This sequential array can be further encoded using run-length encoding to represent the quantized coefficients as alternating values corresponding to lengths of runs of quantized coefficients having a value of zero and quantized coefficients having a non-zero value. These alternating values can be represented as run-val pairs, where each run-val pair comprises a run of zeros followed by a non-zero value. The run-val pairs may themselves be further encoded as run-val codes by applying a run-val mapping table, where each run-val code in the mapping table corresponding to a different run-val pair. The run-val codes may then be further encoded using variable-length encoding based, for example, on a specified Huffman table.
The present invention is directed to an efficient approach to run-length encoding of image signals using run-val pairs.
Further objects and advantages of this invention will become apparent from the detailed description of a preferred embodiment which follows.